Osteonecrosis of the hip (ONH) is a debilitating disease that is increasing in incidence worldwide and frequently progresses to collapse of the femoral head and osteoarthritis that necessitates total hip replacement. In the early stages of ONH, various medical and surgical treatments to preserve the integrity of the femoral head including pharmacological agents such as statins and anticoagulants, electromagnetic therapy, weight reduction, protected weight bearing and range of motion exercises have been attempted with limited success and have not prevented collapse or provided lasting improvement. Alternatively, surgical treatments such as core decompression of the necrotic segment are often performed to relieve pain prevent progression at the early stages of ONH, prior to femoral head collapse. However a wide range of the success rates have been reported from 20-70% for the early (pre-collapse) stages. Maintenance of sphericity of the patient's own femoral head requires both mechanical and biological strategies to withstand intermittent loading and, at the same time, reconstitute the necrotic femoral bone segment. To prevent the collapse of the femoral head after core decompression, the removed necrotic tissue could be filled by a graft or implant to facilitate reconstruction of the necrotic area.
A vascularized fibula graft is one current clinical option, but it suffers from several limitations including pain associated with graft harvesting, availability of sufficient transplantable bone, and the possibility of infection as well as donor site morbidity. Currently, the implant manufacturer Zimmer supplies a porous tantalum metal implant as a treatment for early stage ONH. However, the tantalum metal implant will remain in the proximal femur region for the patient's lifespan. Furthermore, studies have reported no evidence of vascular invasion and minimal bone ingrowth (only 1.9%) in such implants, much less than the mean density (26.2%) of adjacent femoral head trabecular bone. A continuous shell of new cortical bone forms around the tantalum implant that blocks vascular and cancellous invasion. This nullifies the purpose of core decompression and leads to a gradual increase in the intramedullary pressure with subsequent pain. Progressive severe pain leads to clinical failure necessitating total hip replacement whereas the presence of the tantalum metallic implant complicates subsequent surgical procedures including total hip replacement.